BACKGROUND OF THE INVENTION
Field of the Invention
[0001] The present invention relates to a device for estimating a road friction state, and
in particular, to a device for estimating a road friction state in which the friction
state of a wheel with respect to a road surface is estimated on the basis of a physical
amount expressing the ease of slippage of the wheel, such as the road µ slope which
is the slope of the friction coefficient between the wheel and the road surface, with
respect to the slip speed.
Description of the Related Art
[0002] Conventionally, there has been proposed a device in which a wheel speed signal is
detected, and the road µ slope is estimated on the basis of the detected wheel speed
signal. In this device, the wheel speed signal is detected in order to estimate the
road µ slope. Thus, the estimated value of the road µ slope is small at times when
the wheel rides over projections or on rough road surfaces such as on packed snow.
Accordingly, the accuracy of estimating the road µ slope is poor.
[0003] For example, as illustrated in Fig. 10, when the wheel rides over a projection while
travelling on an asphalt road, as described above, the wheel speed signal is small.
The estimated value of the road µ slope estimated at this time is small, and is about
the same value as the estimated value of the road µ slope on a low µ road. When the
wheel rides over a projection, there may be cases in which it is judged that the vehicle
is traveling on a low µ road
[0004] A device for estimating a road friction state according to the preamble of claim
1 is known from
EP 0891904 A2.
SUMMARY OF THE INVENTION
[0005] The present invention was developed in consideration of the above facts, and an object
thereof is to provide a device as well as a method for estimating a road friction
state which can accurately estimate the friction state of a wheel with respect to
a road surface, according to independent claims 1 and 7.
[0006] A first aspect of the present invention is a device, for use with a vehicle having
wheels, for estimating a road friction state, said device comprising: a sensor which
detects a wheel speed signal; a filter which receives the signal and passes a portion
of the wheel speed signal having a frequency within a predetermined range, the range
including at least one resonance point or at least one antiresonance point; a computer
which computes a physical amount expressing a magnitude of vibration of a wheel, on
the basis of the portion of the wheel speed signal passed by the filter; an estimator
which estimates a physical amount expressing ease of slippage of the wheel, on the
basis of the portion of the wheel speed signal passed by the filter; and a road friction
state estimator which estimates a friction state of the wheel with respect to a road
surface, on the basis of the physical amount expressing the magnitude of the vibration
of the wheel computed by the computer and the physical amount expressing the ease
of slippage of the wheel estimated by the estimator.
[0007] The sensor of the present invention detects a wheel speed signal. The filter passes,
from the wheel speed signal detected by the sensor, a portion of the wheel speed signal
within a predetermined range which includes at least one resonance point or at least
one antiresonance point and in which the frequency is great than a low frequency region.
[0008] The computer computes a physical amount expressing the magnitude of the vibration
of the wheel, on the basis of the portion of the wheel speed signal extracted by the
filter. The physical amount expressing the magnitude of the vibration of wheel may
be the vibration level or the amplitude of the portion of the wheel speed signal extracted
by the filter.
[0009] The estimator estimates a physical amount expressing the ease of slippage of the
wheel, on the basis of the wheel speed signal detected by the sensor. Here, the physical
amount expressing the ease of slippage of the wheel may be the road µ slope which
is the slope of the friction coefficient µ between the wheel and the road surface
for a slip speed, or may be the braking torque slope which is the slope of the braking
torque for a slip speed, or may be the driving torque slope which is the slope of
the driving torque.
[0010] The relationship between the physical amount expressing the magnitude of the vibration
of the wheel and the physical amount expressing the ease of slippage of the wheel
is determined for each road surface state.
[0011] Thus, the estimator estimates the friction state of the wheel with respect to the
road surface, on the basis of the physical amount expressing the magnitude of the
vibration of the wheel computed by the computer and on the basis of the physical amount
expressing the ease of slippage of the wheel estimated by the estimator.
[0012] The friction state of the wheel with respect to the road surface is estimated on
the basis of the physical amount expressing the magnitude of the vibration of the
wheel and the physical amount expressing the ease of slippage of the wheel. Thus,
the friction state of the wheel with respect to the road surface can be judged accurately.
[0013] The physical amount expressing the magnitude of the vibration of the wheel increases
proportionally to the reciprocal of the physical amount expressing the ease of slippage
of the wheel. Namely, the physical amount expressing the magnitude of the vibration
of the wheel and the physical amount expressing the ease of slippage of the wheel
exhibit an inverse relationship. As a result, even if the friction state of the wheel
with respect to the road surface is estimated on the basis of the physical amount
expressing the magnitude of the vibration the wheel and the physical amount expressing
the ease of slippage of the wheel which are determined by extracting a portion of
the wheel speed signal in a low frequency region, the friction state of the wheel
with respect to the road surface cannot be judged accurately.
[0014] Here, in the present invention, in order to estimate the friction state, a portion
of the wheel speed signal in a predetermined range which is greater than a low frequency
region is extracted, and the friction state of the wheel with respect to the road
surface can be judged accurately.
[0015] Another aspect of the present invention is a device, for use with a vehicle having
wheels, for estimating a road friction state, said device comprising: a sensor which
detects a wheel speed signal; an estimator which estimates a physical amount expressing
an ease of slippage of a wheel, on the basis of the wheel speed signal detected by
the sensor; a computer which computes a rate of change in the physical amount expressing
the ease of slippage of the wheel which was estimated by the estimator; and a road
friction state estimator which, on the basis of the physical amount expressing the
ease of slippage of the wheel estimated by the estimator and the rate of change in
the physical amount expressing the ease of slippage of the wheel computed by the computer,
estimates a friction state of the wheel with respect to a road surface.
[0016] The relationship between the physical amount expressing the ease of slippage of the
wheel and the rate of change in the physical amount expressing the ease of slippage
of the wheel is determined for each road surface state.
[0017] The road friction state estimator estimates the friction state of the wheel with
respect to the road surface on the basis of the physical amount expressing the ease
of slippage of the wheel estimated by the estimator and the rate of change in the
physical amount expressing the ease of slippage of the wheel which is computed by
the computer.
[0018] In this way, the friction state of the wheel with respect to the road surface is
estimated on the basis of the physical amount expressing the ease of slippage of the
wheel and the rate of change in the physical amount expressing the ease of slippage
of the wheel. Thus, the friction state of the wheel with respect to the road surface
can be judged accurately.
[0019] In the present invention, in order to estimate the friction state, a portion of the
wheel speed signal in a predetermined range which is greater than low frequency region
is extracted. Thus, the friction state of the wheel with respect to the road surface
can be judged accurately.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020]
Fig. 1 is a block diagram of a first embodiment of the present invention.
Fig. 2 is a graph showing the relationship between frequency and amplitude of a wheel
speed signal.
Fig. 3 is a graph showing the relationship between a vibration level of a wheel speed
signal and a road µ slope on an asphalt road and on a low µ road.
Fig. 4 is a graph showing the relationship between a vibration level of a wheel speed
signal and a road µ slope for each road state.
Fig. 5 is a graph showing frequency characteristics of wheel speed signals.
Fig. 6 is a block diagram of the second embodiment of the present invention.
Fig. 7 is a graph illustrating the relationship between an amplitude of a wheel speed
signal and a road µ slope for each road state.
Fig. 8 is a block diagram of a third embodiment of the present invention.
Fig. 9 is a graph illustrating the relationship between a road µ slope and a rate
of change in the road µ slope for each road state.
Fig. 10 is a graph illustrating changes in an estimated value of road µ slope at a
time when a wheel rides over a projection before travelling on a low µ road.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0021] A first embodiment of the present invention will be described hereinafter with reference
to the drawings.
[0022] Fig. 1 illustrates the structure of a device for estimating road friction relating
to a first embodiment. As is shown in Fig. 1, the device for estimating road friction
includes a wheel speed detecting unit 1, a pre-processing filter 2, a transfer function
identifying unit 3, and µ slope computing unit 4. The wheel speed detecting unit 1
detects a wheel speed signal ω
1 of each wheel. The pre-processing filter 2 detects a wheel speed vibration Δω
1 of each wheel as a response output of a wheel resonance system which receives road
disturbance ΔT
d from the detected wheel speed signal ω
1 of each wheel. The transfer function identifying unit 3, by using the method of least
squares, identifies the transfer function for each wheel which satisfies the detected
wheel speed vibration ω
1. The µ slope computing unit 4 computes, for each wheel, the slope of a friction coefficient
µ between the tire and the road, on the basis of the identified transfer function.
[0023] The wheel speed detecting unit 1 in Fig. 1 is formed by a wheel speed sensor which
outputs a sensor output signal corresponding to the wheel speed, and a computing section
which computes the actual rotational speed signal of each wheel from the sensor output
signal.
[0024] The pre-processing filter 2 may be a bandpass filter which allows passage of only
frequency components of a given band centered about a frequency which is estimated
to be the resonance frequency of the wheel resonance system, or may be a high pass
filter which allows passage of only wavelength components of a high band including
the resonance frequency component. In the present embodiment, the parameters prescribing
the frequency characteristic of the bandpass filter or the high pass filter are fixed
at constant values.
[0025] Direct current components are removed from the output of the pre-processing filter
2. Namely, only the wheel speed vibration Δω
1 around the wheel speed signal ω
1 is extracted.
[0026] Here, the transfer function F(s) of the pre-processing filter 2 is
wherein c
i is a coefficient of the filter transfer function, and s is a Laplace operator.
[0027] Next, the transfer function identifying unit 3 derives a dependent computation formula.
In the present embodiment, the computation of the pre-processing filter 2 is included
in the computation of the transfer function identifying unit 3.
[0028] First, the transfer function which is to be identified in the present first embodiment
is modeled two-dimensionally by using the road disturbance ΔT
d as the excitation input and the wheel speed vibration Δω
1 detected by the pre-processing filter 2 at this time as the response output. Namely,
the following vibration model is postulated.
Here, v is the observed noise included at the time of observing the wheel speed signal.
By transforming formula (2), the following formula is obtained.
[0029] First, the formula obtained by using the pre-processing filter of formula (1) on
formula (3) is discretized. At this time, Δω
1, ΔT
d, and v are expressed as discretized data Δω
1(k), ΔT
d(k), and v(k) sampled for each sampling period Ts (wherein k is the sampling number;
k = 1, 2, 3, ...). Further, the Laplace operator s can be discretized by using a predetermined
discretizing method. In the present embodiment, as one example, discretizing is carried
out by the following bilinear conversion. Note that d is a 1 sample delay operator.
[0031] In order to identify the transfer function from each data of the wheel speed vibration
Δω
1 on the basis of the least squares method, formula (4) is converted as per the following
formulas so as to be in the form of a linear function relating to the parameters to
be identified. Note that the subscript "
T" denotes transposition of the matrix.
Here,
In the above formulas, θ is the parameter of the transfer function to be identified.
[0032] Further, the device for estimating a road friction state of the present embodiment
is provided with a bandpass filter 5 which passes, from the wheel speed signal detected
by the wheel speed detecting unit, a portion of the wheel speed signal in a predetermined
range whose frequency, which includes at least one resonance point or at least one
antiresonance point and at which the frequency is greater than a low frequency region.
A vibration level computing unit 6A is connected to the bandpass filter 5. On the
basis of the vehicle speed signal extracted by the bandpass filter 5, the vibration
level computation unit 6A computes a physical amount expressing the magnitude of the
vibration of the wheel (in the present embodiment, the vibration level computation
unit 6A computes the vibration level). The device for estimating a road friction state
of the present first embodiment also includes a road friction state estimating unit
7 which estimates the friction state of the wheel with respect to the road surface
on the basis of the road µ slope computed by the µ slope computing unit 4 and on the
basis of the vibration level computed by the vibration level computing unit 6A.
[0033] Next, operation of the present embodiment will be described.
[0034] In the transfer function identifying unit 3, for each of the data obtained by successively
adapting the discretized data of the detected wheel speed vibration Δω
1 to formula (11), an unknown parameter θ is estimated by applying the method of least
squares, and the transfer function is thereby identified.
[0035] Specifically, the detected wheel speed vibration Δω
1 is converted into digitized data Δω(k) (k= 1, 2, 3, ..), N of these data are sampled,
and the parameter θ of the transfer function is estimated by using the method of least
squares of the following formula.
[0036] Here, the amounts which are designated by being topped with a carat ("^") are the
estimated values.
[0038] Here, ρ is a so-called forgetting coefficient, and is usually set to a value of between
0.95 and 0.99. At this time, it suffices if the initial value is:
wherein α is a sufficiently large positive number.
[0039] Any of various correction methods of least squares may be used as the method for
reducing the error in estimation of the above method of least squares. In the present
embodiment, an example which uses an auxiliary variable method, which is a method
of least squares in which an auxiliary variable is introduced, is described. In accordance
with this method, the parameter of the transfer function is estimated, by using the
following formula, with the m(k) in the step in which the relationship of formula
(9) was obtained serving as an auxiliary variable.
[0041] The principles of the auxiliary variable method are as follows. By substituting equation
(15) into equation (16), then
[0042] Thus, if the auxiliary variable is selected such that the second item at the right
side in formula (19) becomes zero, the estimated value of θ is equal to the true value
of θ. Here, in the present embodiment, the auxiliary variable is a variable which
has been delayed to the extent that there is no correlation between the formula error
r(k) and ζ(k) = [-ξ
y1(k) - ξ
y2(k)]
T. Namely,
wherein L is the delay time.
[0043] After the transfer function is identified as described above, at the µ slope computing
unit 4, a physical amount relating to the road µ slope Do is computed as follows.
When the physical amount relating to the road µ slope D
0 can be computed by formula (21) in this way, if the physical amount is small for
example, it can easily be determined that the friction characteristic between the
tire and the road surface is in a saturated state.
[0044] When the detected wheel speed signal is divided in accordance with the frequency
by the wheel speed detecting unit 1, as illustrated in Fig. 2, the detected wheel
speed signal has two resonance points and one antiresonance point. Of the two resonance
points, the resonance point at the lower frequency side is a longitudinal resonance
point based on tire inertia or the like, and the frequency is f
1 (15-20) Hz. Further, of the two resonance points, the resonance point at the higher
frequency side is a torsional resonance point, and the frequency is f
3 (35-40) Hz. The vehicle speed signal has an antiresonance point in a band which is
insensitive with respect to various signals, and the frequency f
2 is (20-25) Hz. The bandpass filter 5 relating to the present embodiment extracts
a portion of the wheel speed signal of a predetermined range Δf which includes the
torsional resonance point (frequency f
3), from the wheel speed signal detected by the wheel speed detecting unit 1. Note
that the bandpass filter 5 may extract, other than the torsional resonance point,
a portion of the wheel speed signal of the predetermined range Δf, which includes,
rather than the torsional resistance point, the longitudinal resonance point or the
antiresonance point.
[0045] The vibration level computing unit 6A computes the vibration level G(N) of the wheel
speed signal determined by the following formula. The output of the band pass filter
5 is ω(k).
wherein ρ is the forgetting coefficient and is equal to approximately 0.99.
[0046] The vibration level computing unit 6A actually successively computes the gradualizing
formula
at each computation timing. The reason why the vibration level is computed at the
vibration level computing unit 6A is that, as described previously, the road µ slope
is not estimated accurately due to the wheel riding over a projection or the like
(see Fig. 10).
[0047] On the other hand, when the vibration levels and estimated values of the road µ slope
obtained in this way are plotted for an asphalt road surface and for a road surface
of a low µ road, as shown in Fig. 3, the asphalt road surface and the road surface
of the low µ road can be clearly differentiated and distinguished. Further, even if
the wheel rides over a projection on an asphalt road surface, it can clearly be differentiated
and distinguished from the region of the low µ road. In view of the aforementioned,
the present inventors determined the relationship between the vibration level and
the estimated value of the road µ slope for each of various types of road surface
states. The present inventors obtained experimental results demonstrating that, as
shown in Fig. 4, the vibration level and the estimated value of the road µ slope can
be clearly differentiated and distinguished for each region for each road surface
state, e.g., for each region for each of a low µ road, an asphalt road, a stone pavement
road, a packed snowroad, and a gravel/ungraded road. In other words, for example,
the estimated value of the road µ slope for a packed snow road is a slightly lower
value than that of high µ roads (asphalt roads or stone pavement roads), and the differences
in the regions are expressed by the different vibration levels. A gravel road or the
like is in a region where the vibration level is high, and the estimated value of
the road µ slope is a value which is lower than that for high µ roads.
[0048] The road coefficient state estimating unit 7 estimates the friction state of the
wheel with respect to the road surface on the basis of the vibration level computed
by the vibration level computing unit 6A and the estimated value of the road µ slope
computed by the µ slope computing unit 4, and on the basis of the relationship between
the two (see Fig. 4) for each road surface state.
[0049] In the present embodiment, the bandpass filter 5 extracts, from the wheel speed signal,
a portion of the wheel speed signal at either one of the two resonance points, or
a portion of the wheel speed signal at the antiresonance point. In other words, as
illustrated in Fig. 2, an attempt is made to detect a portion of the wheel speed signal
having a frequency greater than a low frequency region. The reason why an attempt
is made to detect a portion of the wheel speed signal at which the frequency is lower
than a low frequency region is that, as shown in Fig. 2, the portion of the wheel
speed signal at which the frequency is lower than a low frequency region has a great
effect because the error thereof is great, and the road friction state cannot be estimated
accurately.
[0050] Fig. 5 illustrates frequency characteristics of wheel speed signals at times of traveling
on an asphalt road and on a low µ road. Compared with an asphalt road, a low µ road
has convexities and concavities which are extremely small.
[0051] Looking at the resonance characteristic in a vicinity of 40Hz, it can be understood
that, for a low µ road, the vibration level is small as compared with an asphalt road,
and the convex and concave portions of the road surface are well reflected. The strength
of the resonance is low, and it can be estimated by the present method that the road
is a low µ road.
[0052] When the vibration components of the low frequency region (5 Hz or less) are considered,
it is noted that, in this region, the vibration level increases proportionally to
the reciprocal of the road µ slope. Therefore, the vibration level of the portion
of the wheel speed signal in the low frequency region of a low µ road becomes greater
than the vibration level of the portion of the wheel speed signal in the low frequency
region of an asphalt road.
[0053] Accordingly, when the vibration level and the road µ slope are computed on the basis
of the portion of the wheel speed signal in the low frequency region and the road
state is estimated, the following problems arise.
[0054] Namely, the frequency component of the low frequency range depends on the road µ
slope and does not reflect the convex and concave state of an actual road surface.
As a result, a large number of adapting processes is required in order to prepare
a map for judging the road surface.
[0055] The portion of the wheel speed signal in the low frequency region includes vibration
components due to rolling and pitching of the vehicle. Thus, there are cases in which
the road surface state cannot be judged accurately by the traveling conditions.
[0056] For the above reasons, a map for judging the road surface must be prepared in accordance
with the physical parameters of the tire and the vehicle. However, dealing with changes
in physical parameters at times when parts of the vehicle are changed, such as the
changing of a tire or the like, is difficult. In some cases, it may not be possible
to judge the road surface state.
[0057] In contrast, in the present embodiment, a portion of a wheel speed signal in a region
greater than a low frequency region is the object. Thus, the above-described problems
do not arise, and the road surface state can be judged accurately.
[0058] Next, a second embodiment of the present invention will be described with reference
to Fig. 6. The structure of the present second embodiment has structural portions
which are similar to those of the previously-described first embodiment. The same
portions are denoted by the same reference numerals, and description thereof is omitted.
Only the different portions are explained.
[0059] Namely, the device for estimating a road friction state relating to the present second
embodiment is equipped with an amplitude computing unit 6B instead of the vibration
level computing unit 6A relating to the first embodiment.
[0060] Next, operation of the present second embodiment will be described. Because parts
of the operation of the present second embodiment are similar to those of the previously-described
first embodiment, description of the same parts of the operation will be omitted,
and only the different parts of the operation will be described.
[0061] The amplitude computing unit 6B relating to the present second embodiment computes
the amplitude of a portion of a vehicle speed signal of a predetermined frequency
which is extracted by the bandpass filter 5. The specifics are as follows.
[0062] Namely, in order to determine the amplitude of a predetermined frequency f, a value
Si of a sine function and a value Ci of a cosine function described later are used.
[0063] Namely, given that the sampling time is TS,
is determined. Given that the wheel speed signal whose amplitude is to be determined
is y and the value of the wheel speed signal at the time of the present sampling is
y(N), then
wherein
An amplitude A is thereby determined.
[0064] The present inventors discovered that the relationship between the estimated value
of the road µ slope and the amplitude computed as described above is separate for
each region for each road surface state, such that the road surface states can be
clearly differentiated and distinguished.
[0065] The road friction state estimating unit 7 relating to the present second embodiment
estimates the road friction state on the basis of the relationship (see Fig. 7) between
the road µ slope computed by the µ slop computing unit 4 and the amplitude computed
by the amplitude computing unit 6B.
[0066] Next, a third embodiment of the present invention will now be described. Because
the structure of the present third embodiment includes the same portions as the structure
of the previously-described first embodiment, the same portions are denoted by the
same reference numerals, and description thereof will be omitted. Only the portions
that differ will be described.
[0067] The device for estimating a road state relating to the present third embodiment includes
the wheel speed detecting unit 1, the pre-processing filter 2, the transfer function
identifying unit 3, and the µ slope computing unit 4. The device for estimating a
road friction state relating to the present third embodiment also includes a µ slope
change rate computing unit 6C which computes the rate of change in the road µ slope
computed by the µ slope computing unit 4.
[0068] The present inventors found that the rate of change in the road µ slope and the estimated
value of the road µ slope are separate for each region in accordance with the road
surface state such that the road surface states can be clearly distinguished and differentiated,
as illustrated in Fig. 9.
[0069] A road friction state estimating unit 7 relating to the present third embodiment
estimates the friction state of the wheel with respect to the road surface on the
basis of the aforementioned relationship (see Fig. 9) and on the basis of the road
µ slope computed by µ slope computing unit 4 and the rate of change in the road µ
slope computed by the µ slope change rate computing unit 6C.
[0070] In the above-described first through third embodiments, the road µ slope is computed.
However, the present invention is not limited to the same, and a braking torque slope
which is equivalent to the road µ slope may be computed.
[0071] As described above, in the present invention, in order to estimate the friction state
of a wheel with respect to a road surface, a portion of a wheel speed signal of a
predetermined region which is greater than a low frequency region is extracted. Thus,
an excellent effect is achieved in that the friction state of the wheel with respect
to the road surface can be judged accurately.
1. A device, for use with a vehicle having wheels, for estimating a road friction state,
said device comprising:
a sensor (1) which detects a wheel speed signal (ω1);
a pre-processing filter (2) which detects, from the wheel speed signal detected by
the sensor (1), a wheel speed vibration (Δω1) of each wheel as response outputs of a wheel resonance system which receives road
surface disturbance (ΔTd); and
an estimator (4) which estimates a physical amount (D0) expressing ease of slippage of the wheel, on the basis of the portion (Δω1) of the wheel speed signal passed by the pre-processing filter (2), characterised by further comprising:
a filter (5) which receives the signal and passes a portion of the wheel speed signal
having a frequency within a predetermined range (Δf), the range (Δf) including at
least one resonance point (f1, f3) or at least one antiresonance point (f2);
a computer (6A; 6B) which computes a physical amount expressing a magnitude of vibration
of a wheel by road disturbance (ΔTd), on the basis of the portion of the wheel speed signal (ω1) passed by the filter (5); and
a road friction state estimator (7) which estimates a friction state of the wheel
with respect to a road surface, on the basis of the physical amount expressing the
magnitude of the vibration of the wheel by road disturbance computed by the computer
(6A; 68) and the physical amount expressing the ease of slippage of the wheel estimated
by the estimator (4).
2. A device, for use with a vehicle having wheels, for estimating a road friction state
according to claim 1, wherein the physical amount expressing the magnitude of the
vibration of the wheel by road disturbance is a vibration level (G(N)) of the portion
of the wheel speed signal passed by the filter (5).
3. A device, for use with a vehicle having wheels, for estimating a road friction state
according to claim 1, wherein the physical amount expressing the magnitude of the
vibration of the wheel by road disturbance is an amplitude (A) of the portion of the
wheel speed signal passed by the filter (5).
4. A device, for use with a vehicle having wheels, for estimating a road friction state
according to any of claims 1 through 3, said device further comprising:
an estimator (4) which estimates a physical amount expressing an ease of slippage
of a wheel, on the basis of the wheel speed signal detected by the sensor; and
a computer (6C) which computes a rate of change in the physical amount expressing
the ease of slippage of the wheel which was estimated by the estimator (4); wherein
the road friction state estimator (7) estimates a friction state of the wheel with
respect to a road surface, on the basis of the physical amount expressing the ease
of slippage of the wheel estimated by the estimator (4) and the rate of change in
the physical amount expressing the ease of slippage of the wheel computed by the computer
(6C).
5. A device, for use with a vehicle having wheels, for estimating a road friction state
according to any of claims 1 through 4, wherein the estimator (4) which estimates
a physical amount expressing an ease of slippage of the wheel includes:
a transfer function identifier (3) which identifies a transfer function of each wheel
corresponding to the detected wheel speed vibration (Δω1); and
a friction coefficient slope computer (4) which computes, on the basis of the identified
transfer function and for each wheel, a slope (D0) of the coefficient of friction between a tire and a road surface, as the physical
amount expressing ease of slippage.
6. A device, for use with a vehicle having wheels, for estimating a road friction state
according to claim 5, wherein the pre-processing filter (2) is a bandpass filter through
which passes frequency components of a predetermined band whose center is a frequency
estimated to be a frequency of the resonance point.
7. A method of estimating a road friction state comprising the steps of:
detecting a wheel speed signal (ω1);
detecting, from the detected wheel speed signal, a wheel speed vibration (Δω1) of each wheel as response outputs of a wheel resonance system which receives road
surface disturbance (ΔTd); and
estimating a physical amount expressing ease of slippage of the wheel, on the basis
of the passed portion (Δω1) of the wheel speed signal; characterised by further comprising the steps of:
passing, from the detected wheel speed signal, a portion of the wheel speed signal
having a frequency within a predetermined range (Δf) which includes at least one resonance
point (f1, f3) or at least one antiresonance point (f2);
computing a physical amount expressing a magnitude of vibration of a wheel by road
disturbance, on the basis of wheel speed vibration (Δω1); and
estimating a friction state of the wheel with respect to a road surface, on the basis
of the computed physical amount expressing the vibration of the wheel by road disturbance
and the estimated physical amount expressing the ease of slippage of the wheel.
8. A method of estimating a road friction state according to claim 7, wherein the physical
amount expressing the magnitude of the vibration of the wheel by road disturbance
is a vibration level (G(N)) of the passed portion of the wheel speed signal.
9. A method of estimating a road friction state according to claim 7, wherein the physical
amount expressing the magnitude of the vibration of the wheel by road disturbance
is an amplitude (A) of the passed portion of the wheel speed signal.
10. A method of estimating a road friction state according to any of claims 7 through
9,
characterised by further comprising the steps of:
estimating a physical amount expressing ease of slippage of a wheel, on the basis
of the detected wheel speed signal;
computing a rate of change in the estimated physical amount expressing the ease of
slippage of the wheel; and
estimating a friction state of the wheel with respect to a road surface, on the basis
of the estimated physical amount expressing the ease of slippage of the wheel and
the computed rate of change in the physical amount expressing the ease of slippage
of the wheel.
11. A method of estimating a road friction state according to any of claims 7 through
10, wherein the step of estimating a physical amount expressing ease of slippage of
the wheel includes the steps of:
identifying a transfer function of each wheel corresponding to the detected wheel
speed vibration (Δω1); and
computing, on the basis of the identified transfer function and for each wheel, a
slope (D0) of a coefficient of friction between a tire and a road surface, as a physical amount
expressing the ease of slippage.
12. A method of estimating a road friction state according to claim 11, wherein in the
step of detecting a wheel speed vibration of each wheel, frequency components of a
predetermined band whose center is a frequency estimated to be a frequency of the
resonance point, substantially pass therethrough.
1. Vorrichtung zur Verwendung mit einem Fahrzeug mit Rädern und zum Ermitteln eines Straßenreibungszustands,
wobei die Vorrichtung umfasst:
einen Sensor (1), der ein Raddrehzahlsignal (ω1) erfasst;
ein Vorverarbeitungsfilter (2), das aus dem vom Sensor (1) erfassten Raddrehzahlsignal
eine Raddrehzahlschwingung (Δω1) jedes Rades als Reaktionsausgangsgrößen eines Radresonanzsystems
erfasst, das Straßenoberflächen-Einflussgrößen (ΔTd) aufnimmt; und
eine Ermittlungseinheit (4), die auf der Grundlage des vom Vorverarbeitungsfilter
(2) durchgelassenen Anteils (Δω1) des Raddrehzahlsignals eine physikalische Größe (D0) ermittelt, die eine Bereitschaft zum Durchrutschen des Rades ausdrückt, dadurch gekennzeichnet, dass sie darüber hinaus umfasst:
ein Filter (5), welches das Signal empfängt und einen Anteil des Raddrehzahlsignals
mit einer Frequenz innerhalb eines vorbestimmten Bereichs (Δf) durchlässt, wobei der
Bereich (Δf) zumindest einen Resonanzpunkt (f1, f3) oder zumindest einen Antiresonanzpunkt (f2) enthält;
einen Computer (6A; 6B), der auf der Grundlage des vom Filter (5) durchgelassenen
Anteil des Raddrehzahlsignals (ω1) eine physikalische Größe berechnet, die einen Betrag der von straßenbezogenen Einflussgrößen
(ΔTd) herrührenden Schwingung eines Rades ausdrückt; und
eine Straßenreibungszustands-Ermittlungseinheit (7), die einen Reibungszustand des
Rades in Bezug auf eine Straßenoberfläche ermittelt, und zwar auf der Grundlage der
vom Computer (6A; 6B) berechneten physikalischen Größe, die den Betrag der von den
straßenbezogenen Einflussgrößen herrührenden Schwingung des Rades ausdrückt, und auf
der Grundlage der von der Ermittlungseinheit (4) ermittelten physikalischen Größe,
die die Bereitschaft zum Durchrutschen des Rades ausdrückt.
2. Vorrichtung zur Verwendung mit einem Fahrzeug mit Rädern und zum Ermitteln eines Straßenreibungszustands
nach Anspruch 1, wobei die physikalische Größe, die den Betrag der von den straßenbezogenen
Einflussgrößen herrührenden Schwingung des Rades ausdrückt, ein Schwingungspegel (G(N))
des vom Filter (5) durchgelassenen Anteils des Raddrehzahlsignals ist.
3. Vorrichtung zur Verwendung mit einem Fahrzeug mit Rädern und zum Ermitteln eines Straßenreibungszustands
nach Anspruch 1, wobei die physikalische Größe, die den Betrag der von den straßenbezogenen
Einflussgrößen herrührenden Schwingung des Rades ausdrückt, eine Amplitude (A) des
vom Filter (5) durchgelassenen Anteils des Raddrehzahlsignals ist.
4. Vorrichtung zur Verwendung mit einem Fahrzeug mit Rädern und zum Ermitteln eines Straßenreibungszustands
nach einem der Ansprüche 1 bis 3, wobei die Vorrichtung darüber hinaus umfasst:
eine Ermittlungseinheit (4), die auf der Grundlage des vom Sensor erfassten Raddrehzahlsignals
eine physikalische Größe ermittelt, die eine Bereitschaft zum Durchrutschen eines
Rades ausdrückt; und
einen Computer (6C), der eine Änderungsrate der von der Ermittlungseinheit (4) ermittelten
physikalischen Größe berechnet, die die Bereitschaft zum Durchrutschen des Rades ausdrückt;
wobei
die Straßenreibungszustands-Ermittlungseinheit (7) einen Reibungszustand des Rades
in Bezug auf eine Straßenoberfläche ermittelt, und zwar auf der Grundlage der von
der Ermittlungseinheit (4) ermittelten physikalischen Größe, die die Bereitschaft
zum Durchrutschen des Rades ausdrückt, und auf der Grundlage der vom Computer (6C)
berechneten Änderungsrate der physikalischen Größe, die die Bereitschaft zum Durchrutschen
des Rades ausdrückt.
5. Vorrichtung zur Verwendung mit einem Fahrzeug mit Rädern und zum Ermitteln eines Straßenreibungszustands
nach einem der Ansprüche 1 bis 4, wobei die Ermittlungseinheit (4), die eine physikalische
Größe ermittelt, welche eine Bereitschaft zum Durchrutschen des Rades ausdrückt, umfasst:
eine Transferfunktions-Bestimmungseinheit (3), die eine Transferfunktion jedes Rades
entsprechend der erfassten Raddrehzahlschwingung (Δω1) bestimmt; und
eine Reibungskoeffizientengradienten-Berechnungseinheit (4), die auf der Grundlage
der bestimmten Transferfunktion und für jedes Rad als die physikalische Größe, die
die Bereitschaft zum Durchrutschen ausdrückt, einen Gradienten (D0) des Reibungskoeffizienten zwischen einem Reifen und einer Straßenoberfläche berechnet.
6. Vorrichtung zur Verwendung mit einem Fahrzeug mit Rädern und zum Ermitteln eines Straßenreibungszustands
nach Anspruch 5, wobei der Vorverarbeitungsfilter (2) ein Bandpassfilter ist, das
Frequenzkomponenten eines vorbestimmten Bandes durchlässt, dessen Mitte eine Frequenz
ist, die als Frequenz des Resonanzpunkts ermittelt wurde.
7. Verfahren zum Ermitteln eines Straßenreibungszustands, die Schritte umfassend:
Erfassen eines Raddrehzahlsignals (ω1);
Erfassen, aus dem erfassten Raddrehzahlsignal, einer Raddrehzahlschwingung (Δω1) jedes Rades als Reaktionsausgangsgrößen eines Radresonanzsystems, das Straßenoberflächen-Einflussgrößen
(ΔTd) aufnimmt; und
Ermitteln, auf der Grundlage des durchgelassenen Anteils (Δω1) des Raddrehzahlsignals, einer physikalischen Größe, die eine Bereitschaft zum Durchrutschen
des Rades ausdrückt; dadurch gekennzeichnet, dass es darüber hinaus die Schritte umfasst:
Durchlassen, von dem erfassten Raddrehzahlsignal, eines Anteils des Raddrehzahlsignals
mit einer Frequenz innerhalb eines vorbestimmten Bereichs (Δf), der zumindest einen
Resonanzpunkt (f1, f3) oder zumindest einen Antiresonanzpunkt (f2) enthält;
Berechnen einer physikalischen Größe, die einen Betrag einer von straßenbezogenen
Einflussgrößen herrührenden Schwingung eines Rades ausdrückt, auf der Grundlage der
Raddrehzahlschwingung (Δω1); und
Ermitteln eines Reibungszustands des Rades in Bezug auf eine Straßenoberfläche, und
zwar auf der Grundlage der berechneten physikalischen Größe, die die von den straßenbezogenen
Einflussgrößen herrührende Schwingung des Rades ausdrückt, und auf der Grundlage der
ermittelten physikalischen Größe, die die Bereitschaft zum Durchrutschen des Rades
ausdrückt.
8. Verfahren zum Ermitteln eines Straßenreibungszustands nach Anspruch 7,
wobei die physikalische Größe, die den Betrag der von den straßenbezogenen Einflussgrößen
herrührenden Schwingung des Rades ausdrückt, ein Schwingungspegel (G(N)) des durchgelassenen
Anteils des Raddrehzahlsignals ist.
9. Verfahren zum Ermitteln eines Straßenreibungszustands nach Anspruch 7,
wobei die physikalische Größe, die den Betrag der von den straßenbezogenen Einflussgrößen
herrührenden Schwingung des Rades ausdrückt, eine Amplitude (A) des durchgelassenen
Anteils des Raddrehzahlsignals ist.
10. Verfahren zum Ermitteln eines Straßenreibungszustands nach einem der Ansprüche 7 bis
9,
dadurch gekennzeichnet, dass es darüber hinaus die Schritte umfasst:
Ermitteln einer die Bereitschaft zum Durchrutschen eines Rades ausdrückenden physikalischen
Größe auf der Grundlage des erfassten Raddrehzahlsignals;
Berechnen einer Änderungsrate der ermittelten physikalischen Größe, die die Bereitschaft
zum Durchrutschen des Rades ausdrückt; und
Ermitteln eines Reibungszustands des Rades in Bezug auf eine Straßenoberfläche, und
zwar auf der Grundlage der ermittelten physikalischen Größe, die die Bereitschaft
zum Durchrutschen des Rades ausdrückt, und auf der Grundlage der berechneten Änderungsrate
der physikalischen Größe, die die Bereitschaft zum Durchrutschen des Rades ausdrückt.
11. Verfahren zum Ermitteln eines Straßenreibungszustands nach einem der Ansprüche 7 bis
10, wobei der Schritt des Ermittelns einer physikalischen Größe, die die Bereitschaft
zum Durchrutschen des Rades ausdrückt, die Schritte umfasst:
Bestimmen einer Transferfunktion jedes Rades entsprechend der erfassten Raddrehzahlschwingung
(Δω1); und
Berechnen, auf der Grundlage der bestimmten Transferfunktion und für jedes Rad, eines
Gradienten (D0) eines Reibungskoeffizienten zwischen einem Reifen und einer Straßenoberfläche, als
eine physikalische Größe, die die Bereitschaft zum Durchrutschen ausdrückt.
12. Verfahren zum Ermitteln eines Straßenreibungszustands nach Anspruch 11,
wobei in dem Schritt des Erfassens einer Raddrehzahlschwingung jedes Rades Frequenzkomponenten
eines vorbestimmten Bandes im Wesentlichen durchgelassen werden, dessen Mitte eine
Frequenz ist, die als Frequenz des Resonanzpunkts ermittelt wurde.
1. Dispositif, pour une utilisation avec un véhicule comportant des roues, pour estimer
un état de frottement de route, ledit dispositif comprenant :
un capteur (1) qui détecte un signal de vitesse de roue (ω1) ;
un filtre de prétraitement (2) qui détecte, à partir du signal de vitesse de roue
détecté par le capteur (1), une vibration de vitesse de roue (Δω1) de chaque roue en tant que sorties de réponse d'un système de résonance de roue
qui reçoit une perturbation de revêtement routier (ΔTd) ; et
un estimateur (4) qui estime une quantité physique (D0) exprimant une facilité de patinage de la roue, sur la base de la partie (Δω1) du signal de vitesse de roue qui est passée à travers le filtre de prétraitement
(2), caractérisé en ce qu'il comprend en outre :
un filtre (5) qui reçoit le signal et laisse passer une partie du signal de vitesse
de roue ayant une fréquence dans une plage prédéterminée (Δf), la plage (Δf) comprenant
au moins un point de résonance (f1 f3) ou au moins un point d'antirésonance (f2) ;
un ordinateur (6A ; 6B) qui calcule une quantité physique exprimant une amplitude
de vibration d'une roue par une perturbation de route (ΔTd), sur la base de la partie du signal de vitesse de roue (ω1 qui est passée à travers le filtre (5) ; et
un estimateur d'état de frottement de route (7) qui estime un état de frottement de
la roue par rapport à un revêtement routier, sur la base de la quantité physique exprimant
l'amplitude de la vibration de la roue par une perturbation de route calculée par
l'ordinateur (6A ; 6B) et de la quantité physique exprimant la facilité de patinage
de la roue estimée par l'estimateur (4).
2. Dispositif, pour une utilisation avec un véhicule comportant des roues, pour estimer
un état de frottement de route selon la revendication 1, dans lequel la quantité physique
exprimant l'amplitude de la vibration de la roue par une perturbation de route est
un niveau de vibration (G(N)) de la partie du signal de vitesse de roue qui est passée
à travers le filtre (5).
3. Dispositif, pour une utilisation avec un véhicule comportant des roues, pour estimer
un état de frottement de route selon la revendication 1, dans lequel la quantité physique
exprimant l'amplitude de la vibration de la roue par une perturbation de route est
une amplitude (A) de la partie du signal de vitesse de roue qui est passée à travers
le filtre (5).
4. Dispositif, pour une utilisation avec un véhicule comportant des roues, pour estimer
un état de frottement de route selon l'une quelconque des revendications 1 à 3, ledit
dispositif comprenant en outre :
un estimateur (4) qui estime une quantité physique exprimant une facilité de patinage
d'une roue, sur la base du signal de vitesse de roue détecté par le capteur ; et
un ordinateur (6C) qui calcule un taux de variation de la quantité physique exprimant
la facilité de patinage de la roue qui a été estimée par l'estimateur (4) ; dans lequel
l'estimateur d'état de frottement de route (7) estime un état de frottement de la
roue par rapport à un revêtement routier, sur la base de la quantité physique exprimant
la facilité de patinage de la roue estimée par l'estimateur (4) et du taux de variation
de la quantité physique exprimant la facilité de patinage de la roue calculée par
l'ordinateur (6C).
5. Dispositif, pour une utilisation avec un véhicule comportant des roues, pour estimer
un état de frottement de route selon l'une quelconque des revendications 1 à 4, dans
lequel l'estimateur (4), qui estime une quantité physique exprimant une facilité de
patinage de la roue, comprend :
un identifiant de fonction de transfert (3) qui identifie une fonction de transfert
de chaque roue correspondant à la vibration de vitesse de roue détectée (Δω1) ; et
un calculateur de pente de coefficient de frottement (4) qui calcule, sur la base
de la fonction de transfert identifiée et pour chaque roue, une pente (D0) du coefficient de frottement entre un pneu et un revêtement routier, en tant que
quantité physique exprimant la facilité de patinage.
6. Dispositif, pour une utilisation avec un véhicule comportant des roues, pour estimer
un état de frottement de route selon la revendication 5, dans lequel le filtre de
prétraitement (2) est un filtre passe-bande à travers lequel passent les composantes
de fréquence d'une bande prédéterminée dont le centre est une fréquence estimée comme
étant une fréquence du point de résonance.
7. Procédé d'estimation d'un état de frottement de route comprenant les étapes consistant
à :
détecter un signal de vitesse de roue (ω1) ;
détecter, à partir du signal de vitesse de roue détecté, une vibration de vitesse
de roue (Δω1) de chaque roue en tant que sorties de réponse d'un système de résonance de roue
qui reçoit une perturbation de revêtement routier (ΔTd) ; et
estimer une quantité physique exprimant une facilité de patinage de la roue, sur la
base de la partie passée (Δω1) du signal de vitesse de roue ; caractérisé en ce qu'il comprend en outre les étapes consistant à :
laisser passer, à partir du signal de vitesse de roue détecté, une partie du signal
de vitesse de roue ayant une fréquence dans une plage prédéterminée (Δf) qui comprend
au moins un point de résonance (f1, f3) ou au moins un point d'antirésonance (f2) ;
calculer une quantité physique exprimant une amplitude de vibration d'une roue par
une perturbation de route, sur la base de la vibration de vitesse de roue (Δω1) ; et
estimer un état de frottement de la roue par rapport à un revêtement routier, sur
la base de la quantité physique calculée exprimant la vibration de la roue par une
perturbation de route et de la quantité physique estimée exprimant la facilité de
patinage de la roue.
8. Procédé d'estimation d'un état de frottement de route selon la revendication 7, dans
lequel la quantité physique exprimant l'amplitude de la vibration de la roue par une
perturbation de route est un niveau de vibration (G(N)) de la partie passée du signal
de vitesse de roue.
9. Procédé d'estimation d'un état de frottement de route selon la revendication 7, dans
lequel la quantité physique exprimant l'amplitude de la vibration de la roue par une
perturbation de route est une amplitude (A) de la partie passée du signal de vitesse
de roue.
10. Procédé d'estimation d'un état de frottement de route selon l'une quelconque des revendications
7 à 9,
caractérisé en ce qu'il comprend en outre les étapes consistant à :
estimer une quantité physique exprimant une facilité de patinage d'une roue, sur la
base du signal de vitesse de roue détecté ;
calculer un taux de variation de la quantité physique estimée exprimant la facilité
de patinage de la roue ; et
estimer un état de frottement de la roue par rapport à un revêtement routier, sur
la base de la quantité physique estimée exprimant la facilité de patinage de la roue
et du taux de variation calculé de la quantité physique exprimant la facilité de patinage
de la roue.
11. Procédé d'estimation d'un état de frottement de route selon l'une quelconque des revendications
7 à 10, dans lequel l'étape d'estimation d'une quantité physique exprimant une facilité
de patinage de la roue comprend les étapes consistant à :
identifier une fonction de transfert de chaque roue correspondant à la vibration de
vitesse de roue détectée (Δω1) ; et
calculer, sur la base de la fonction de transfert identifiée et pour chaque roue,
une pente (D0) d'un coefficient de frottement entre un pneu et un revêtement routier, en tant que
quantité physique exprimant la facilité de patinage.
12. Procédé d'estimation d'un état de frottement de route selon la revendication 11, dans
lequel, à l'étape de détection d'une vibration de vitesse de roue de chaque roue,
les composantes de fréquence d'une bande prédéterminée, dont le centre est une fréquence
estimée comme étant une fréquence du point de résonance, passent sensiblement à travers
celui-ci.